/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package core.net;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

/**
 * A cached implementation of DNSToSwitchMapping that takes an raw
 * DNSToSwitchMapping and stores the resolved network location in a cache. The
 * following calls to a resolved network location will get its location from the
 * cache.
 * 
 */
public class CachedDNSToSwitchMapping implements DNSToSwitchMapping {
	private Map<String, String> cache = new ConcurrentHashMap<String, String>();
	protected DNSToSwitchMapping rawMapping;

	public CachedDNSToSwitchMapping(DNSToSwitchMapping rawMapping) {
		this.rawMapping = rawMapping;
	}

	public List<String> resolve(List<String> names) {
		// normalize all input names to be in the form of IP addresses
		names = NetUtils.normalizeHostNames(names);

		List<String> result = new ArrayList<String>(names.size());
		if (names.isEmpty()) {
			return result;
		}

		// find out all names without cached resolved location
		List<String> unCachedHosts = new ArrayList<String>(names.size());
		for (String name : names) {
			if (cache.get(name) == null) {
				unCachedHosts.add(name);
			}
		}

		// Resolve those names
		List<String> rNames = rawMapping.resolve(unCachedHosts);

		// Cache the result
		if (rNames != null) {
			for (int i = 0; i < unCachedHosts.size(); i++) {
				cache.put(unCachedHosts.get(i), rNames.get(i));
			}
		}

		// Construct the result
		for (String name : names) {
			// now everything is in the cache
			String networkLocation = cache.get(name);
			if (networkLocation != null) {
				result.add(networkLocation);
			} else { // resolve all or nothing
				return null;
			}
		}
		return result;
	}
}
